This invention relates to planar magnetic components, and more particularly relates to such components which include a core and a planar winding structure, such as planar inductors and transformers.
Planar magnetic components, particularly those characterized by relatively high leakage flux, such as inductors and some transformers designed to have built-in inductance, are useful in power electronics applications in which space is limited, for example, electronic lamp ballasts and switched-mode power supplies.
Conventional planar magnetic components have winding structures which consist of a stack of layers each containing part of the total winding structure, insulating layers usually consisting of a flexible, non-conducting, low permittivity, high temperature resistant polymer to prevent electrical contact between the turns in adjacent layers, and a contacting structure that permits electrical contact between turns in adjacent layers where needed. The winding structures are usually made by etching or stamping or sometimes by folding. Contacts are usually made by soldering or via plating.
An improved planar magnetic component with planar winding structure which is compact, in which the winding layers are readily interconnected, and which can be readily connected to external circuitry, is described and claimed in co-pending U.S. patent application Ser. No. 08/874,171 (Attorney docket number PHA 23,256) filed Jun. 13, 1997, and assigned to the present assignee. The density of the planar winding structure results in a relatively low thermal resistance, compensating somewhat for the lower surface area available for heat transfer.
Winding losses occur in all such magnetic components. In general, winding losses are due to the interaction of the winding current with a local magnetic field, due largely to leakage flux from the windings and to stray fields near the gaps in the core. The leakage flux, defined as the magnetic flux not present in either the core or the gaps, is relatively high in inductors as well as in some transformers, which are designed to have built-in inductance, such as those sometimes used in switched mode power supplies and lamp ballasts.
In such high-leakage flux applications, there is a need to reduce the winding losses, while at the same time preserving or even enhancing the advantages of the known planar magnetic components.